@ PGit
At the local computer fair a company called Sky Computers sells nice setups for reasonable prices. Their bottom-of-the-range computer will be okay for you. The specs:
AMD Sempron 2600
256mb RAM
80gb HD
onboard graphics 64mb (can add a card later via AGP)
DVD ROM / CD Writer combo
modem and 10/100 network
keyboard, mouse, speakers
How much? £220.
(no monitor, that is extra. They do a 19" TFT flatscreen for £175)
PM me if you want their contact details. (They might deliver so you don't have to come to the fair in London)